Research is proposed to investigate the role of Pavlovian processes in the prevention ("immunization") and alleviation ("therapy") of the deleterious effects of chronic exposure to uncontrollable aversive events. Previous research, involving multiple sessions of exposure to uncontrollable shock, has identified Pavlovian conditioning to shock cues and the resultant development of stimulus control, as being critical to the maintenance and expression of uncontrollable shock-produced escape deficits and analgesia. The central thesis of the proposed research is that Pavlovian, rather than operant, contingencies will likewise determine the effects of immunization and therapy treatments when exposure is chronic. The first project includes three experiments in which immunization should occur on the basis of operant contingencies (i.e., rats experience controllable shock prior to uncontrollable shock), but failure to immunize is predicted on the basis of Pavlovian contingencies. Additionally, two experiments are proposed in which immunization-like outcomes are expected on the basis of Pavlovian manipulations, despite consistent exposure to uncontrollable shock only. The second project proposes four experiments designed to accomplish therapy by counteracting prior Pavlovian conditioning to a signal for uncontrollable shock. The "therapeutic" procedures include Pavlovian extinction, an inhibitory conditioning procedure, exposure to uncorrelated presentations of shock with the prior shock signal, and counterconditioning to the signal by the use of controllable shock. In addition to the contribution these studies will make toward understanding the nature of interactions between Pavlovian and operant contingencies over time, they offer considerable promise for the development of alternative behavioral interventions designed to minimize the adverse consequences of chronic uncontrollable stress.